Seat frame for vehicle seat

ABSTRACT

A bracket for attaching an actuator is easily bonded to a side frame while avoiding interference with a shaft for driving a reclining mechanism. In a seat side frame which is provided at each of both ends of a seat back frame in the width direction, a reclining mechanism, and an actuator, the reclining mechanism is attached to a side wall of the side frame, and the actuator is fixed to an attachment bracket bonded to an inner surface of a portion to which the reclining mechanism is attached in the side wall in the width direction. An upper portion which is disposed above the attachment portion of the reclining mechanism and a lower portion which is disposed below the attachment portion thereof are connected to each other at the rear ends thereof and are separated from each other at the front ends thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/222,103, filed Apr. 5, 2021, which is a continuation of U.S. patentapplication Ser. No. 16/834,056, filed Mar. 30, 2020, now U.S. Pat. No.10,967,770, which is a continuation of U.S. patent application Ser. No.16/389,387, filed Apr. 19, 2019, now U.S. Pat. No. 10,604,044, which isa continuation of U.S. patent application Ser. No. 15/810,970, filedNov. 13, 2017, now U.S. Pat. No. 10,266,087, which is a divisional ofU.S. patent application Ser. No. 15/249,960, filed Aug. 29, 2016, nowU.S. Pat. No. 9,815,397, which is a divisional of U.S. patentapplication Ser. No. 14/424,312, filed Feb. 26, 2015, now U.S. Pat. No.9,428,084, which is the U.S. national phase of the International PatentApplication No. PCT/JP2012/072387, filed Sep. 3, 2012, the entirecontent of all being incorporated herein by reference.

BACKGROUND

Disclosed herein is a seat frame for a vehicle seat, and particularly, aseat frame for a vehicle seat in which a reclining mechanism and anactuator for driving the reclining mechanism are attached to each ofside frames disposed at both right and left ends of a seat back frame.

In a reclining mechanism which rotates a seat back with respect to aseat cushion in a seat frame for a vehicle seat, there is known anelectric reclining mechanism which is operated by a driving forceapplied from an actuator as another member (for example, see JapanesePatent Document No. 2006-306188 A (“the '188 Document”).

The reclining mechanism disclosed in the '188 Document includes a shaftwhich penetrates a reclining mechanism body, and the shaft is insertedin a through-hole formed in a side frame. An actuator which is disposedat an inner side of each of the right and left side frames is attachedto a portion of the shaft which protrudes from the through-hole. Here,an output shaft of the actuator is engaged with the shaft. Thus, whenthe actuator is driven, the output shaft rotates along with the shaft,and hence the driving force generated from the actuator is transmittedto the reclining mechanism.

In the reclining mechanism disclosed in the '188 Document, the actuatoris fixed to a predetermined portion of the seat frame by a bolt in orderto regulate the rotation of the actuator when the actuator is driven.

As illustrated in the '188 Document, the reclining mechanism isgenerally attached to each of the side frames disposed at both right andleft ends of the seat back frame, in particular, to lower ends connectedto a seat cushion frame. Further, in the '188 Document, a bolt hole isformed in the vicinity of the arrangement space of the actuator in theside frame in order to fasten the bolt for stopping the rotation of theactuator to the side frame. In addition, in the '188 Document, areinforcement bracket is bonded to a portion of the side frame, which isprovided with the bolt hole.

In the case where the reinforcement bracket is bonded to the side frame,it is desirable that the reinforcement bracket can be easily attached tothe side frame. However, in the case of bonding the reinforcementbracket to the side frame, there is a concern that the shaft rotating todrive the reclining mechanism may interfere with the reinforcementbracket. Thus, the reinforcement bracket is required to have a shape tobe easily bonded to the side frame while avoiding the interference withthe shaft.

Further, it is desirable that the number of components of the vehicleseat is small as much as possible. For this, it is beneficial todecrease the number of components in the structure where thereinforcement bracket is provided.

Further, in the case of bonding the reinforcement bracket to the sideframe by welding, the welding area needs to be set so that thepositional relation between the bolt for fixing the actuator and theshaft is stable without varying. It is desirable to set the welding areabetween the reinforcement bracket and the side frame so that the weldingoperation is easily performed.

Further, there is a need to ensure the rigidity of the reinforcementbracket itself in order to stabilize the bonded state between thereinforcement bracket and the side frame. For that reason, it isbeneficial to secure the rigidity of the reinforcement bracket whileconsidering the interference of the reinforcement bracket with respectto the actuator during the attachment of the actuator.

Moreover, in the case where a rotation shaft of an armrest is supportedby the side frame in the vehicle seat equipped with the armrest, thereis a need to provide the reinforcement bracket in consideration of theload generated in the side frame by the rotation of the armrest.

SUMMARY

Therefore, various embodiments of the invention are made in view of theabove-described problems, and an object thereof is to provide a seatframe for a vehicle seat which allows a bracket for attaching anactuator to be easily attached to a side frame while avoiding aninterference with a shaft for driving a reclining mechanism.

Further, another object is to provide a seat frame for a vehicle seatwhich can decrease the number of components while providing a bracketfor attaching an actuator.

Further, another object is to provide a seat frame for a vehicle seat inwhich a welding area is set to stabilize a positional relation between abolt for fixing an actuator and a shaft for driving a recliningmechanism when a bracket for attaching an actuator is bonded to a sideframe by welding. Particularly, another object is to provide a seatframe for a vehicle seat in which a welding area is appropriately set sothat a welding operation is easily performed.

Further, another object is to provide a seat frame for a vehicle seatwhich can improve the rigidity of a bracket while it is taken intoconsideration that a bracket for attaching an actuator does notinterfere with the actuator.

Furthermore, another object is to provide a seat frame for a vehicleseat, which includes a bracket being for attaching an actuator andhaving a shape devised in consideration of a load generated in a sideframe by the rotation of an armrest in the vehicle seat including thearmrest.

The above-described problems may be solved by a seat frame for a vehicleseat, including: a side frame which is disposed at each of both ends ofa seat back frame of a seat back of the vehicle seat in the widthdirection of the vehicle seat; a reclining mechanism which includes arotation shaft extending in the width direction and pivots the seat backwith respect to a seat cushion of the vehicle seat by the rotation ofthe rotation shaft; and an actuator which is driven to rotate therotation shaft, wherein the reclining mechanism is attached to a sidewall while the rotation shaft penetrates the side wall of the sideframe, wherein the actuator is fixed to an attachment bracket bonded toan inner surface of the side wall in the width direction while engagingwith a portion of the rotation shaft penetrating the side wall of theside frame, wherein the attachment bracket includes an upper portionwhich is disposed above the attachment area of the reclining mechanismin the side wall and a lower portion which is disposed below theattachment area of the reclining mechanism in the side wall, and whereinone end of the upper portion and one end of the lower portion in thefront to back direction of the vehicle seat are connected to each other,and the other end of the upper portion and the other end of the lowerportion in the front to back direction are separated from each other.

According to the above-described configuration, since the shape of theattachment bracket of the actuator is formed as a shape that avoids theattachment area of the reclining mechanism in the side wall of the sideframe, the attachment bracket may be bonded to the side frame whileavoiding the interference with the rotation shaft for driving thereclining mechanism. Further, since one end of the attachment bracket inthe front to back direction is opened, the attachment bracket may beeasily bonded to the side frame while avoiding the interference with therotation shaft.

Further, the seat frame for the vehicle seat may further include aconnection frame which connects the lower ends of the side frames toeach other, and the attachment bracket may be disposed at each of bothends of the connection frame and may be integrated with the connectionframe.

According to the above-described configuration, the end of theconnection frame serves as the attachment bracket. That is, the numberof components may be decreased compared to the configuration in whichthe attachment bracket is provided as a separate member.

Further, in the seat frame for the vehicle seat, the upper portion maybe provided with a bolt hole for fixing the actuator, and a portion,which is located between the bolt hole and the attachment area of thereclining mechanism in the side wall, in the upper portion may be weldedto the side wall.

According to the above-described configuration, since the attachmentbracket is welded to the side frame at the position between the bolthole and the attachment area of the reclining mechanism, a welding areaexists between the bolt hole and the rotation shaft for driving thereclining mechanism. Accordingly, since the positions of the bolt holeand the rotation shaft do not easily change, the positional relationbetween the bolt for fixing the actuator and the rotation shaft isstabilized.

Further, in the seat frame for the vehicle seat, an area in which thereclining mechanism is attached to the side wall may be formed as acircular area when viewed from the width direction, and the attachmentbracket may be formed in a C-shape that follows the outer edge of theattachment portion of the reclining mechanism in the side wall whenviewed from the width direction.

According to the above-described configuration, the attachment bracketmay be effectively bonded to the side frame in response to the outeredge of the attachment portion of the reclining mechanism in the sidewall of the side frame.

Further, in the seat frame for the vehicle seat, the upper portion andthe lower portion may be respectively welded to the side wall, at leasta portion of the welding area between the upper portion and the sidewall may be located in front of the rotation shaft, and at least aportion of the welding area between the lower portion and the side wallmay be located behind the rotation shaft.

According to the above-described configuration, each of the upperportion and the lower portion of the attachment bracket may besatisfactorily bonded to the side wall of the side frame. Further, sinceeach welding area extends in the front to back direction of the vehicleseat, the rigidity with respect to the load exerted in the front to backdirection may be ensured. Accordingly, it is possible to stably maintaina state where each of the upper portion and the lower portion of theattachment bracket is bonded to the side wall of the side frame.

Further, in the seat frame for the vehicle seat, the upper end of theattachment bracket may be provided with a bent portion which is bentinward in the width direction.

According to the above-described configuration, since the bent portionis formed in the attachment bracket, the rigidity of the attachmentbracket is improved.

Moreover, in the seat frame for the vehicle seat in which the bentportion is formed in the attachment bracket, the upper portion may beprovided with the bolt hole for fixing the actuator, and a portion,which is adjacent to the portion provided with the bolt hole in theattachment bracket, in the bent portion may have an inward extensionamount in the width direction shorter than the portion which is notadjacent to the portion provided with the bolt hole.

A portion which is adjacent to the portion provided with the bolt holein the bent portion faces a portion of the actuator, specifically, thevicinity of the attachment portion of the fixed bolt. Thus, when theextension amount of the portion which is adjacent to the portionprovided with the bolt hole in the bent portion is short as in theabove-described configuration, the bent portion may be formed whilesuppressing the interference with the actuator.

Further, in the seat frame for the vehicle seat, a portion, which islocated above the attachment bracket, in the side wall may support arotation shaft used when an armrest of the vehicle seat rotates withrespect to the seat back, the upper portion may include an extensionportion which extends upward toward the rotation shaft, and theextension portion may be provided in front of the rotation shaft.

When the armrest rotates in the case where the rotation shaft of thearmrest is supported by the side wall of the side frame, a load isapplied to a portion which is located in front of the rotation shaft inthe side frame. In contrast, in the above-described configuration, theextension portion in which the upper portion of the attachment bracketextends upward toward the rotation shaft is provided at the frontposition of the rotation shaft. Accordingly, it is possible to improvethe rigidity of the side frame with respect to the load generated whenthe armrest rotates.

Further, in the seat frame for the vehicle seat in which the extensionportion is provided in the upper portion of the attachment bracket, therear end of the side wall may be provided with a fragile portion whichis deformed so that the side frame is inclined backward when a collisionload is applied from the rear side, and the extension portion may beprovided in front of the fragile portion.

According to the above-described configuration, since the extensionportion is provided at the front position of the fragile portion inorder to avoid the fragile portion, the fragile portion issatisfactorily deformed when a collision load is applied to the vehicleseat from the rear side.

According to the seat frame for the vehicle seat of an embodiment of theinvention, the attachment bracket is easily bonded to the side framewhile avoiding the interference with the rotation shaft for driving thereclining mechanism.

According to the seat frame for the vehicle seat of an embodiment of theinvention, the number of components is small compared to theconfiguration in which the attachment bracket is provided as a separatemember.

According to the seat frame for the vehicle seat of an embodiment of theinvention, since the positions of the bolt hole and the rotation shaftmay not easily change, the positional relation between the bolt forfixing the actuator and the rotation shaft is stabilized.

According to the seat frame for the vehicle seat of an embodiment of theinvention, the attachment bracket is effectively bonded to the sideframe in response to the outer edge of the attachment area of thereclining mechanism in the side wall of the side frame.

According to the seat frame for the vehicle seat of an embodiment of theinvention, each of the upper portion and the lower portion of theattachment bracket is satisfactorily bonded to the side wall of the sideframe. Further, it is possible to stably maintain a state where each ofthe upper portion and the lower portion of the attachment bracket isbonded to the side wall of the side frame.

According to the seat frame for the vehicle seat of an embodiment of theinvention, the rigidity of the attachment bracket is improved.

According to the seat frame for the vehicle seat of an embodiment of theinvention, the bent portion may be formed while suppressing theinterference with the actuator.

According to the seat frame for the vehicle seat of an embodiment of theinvention, the rigidity of the side frame is improved with respect tothe load generated in the side frame during the rotation of the armrest.

According to the seat frame for the vehicle seat of an embodiment of theinvention, the fragile portion is satisfactorily deformed when thecollision load is applied to the vehicle seat from the rear side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view illustrating an appearance of a vehicleseat according to an embodiment of the invention;

FIG. 2 is a perspective view illustrating an entire seat frame for thevehicle seat according to the embodiment of the invention;

FIG. 3 is a rear view illustrating the seat frame for the vehicle seataccording to the embodiment of the invention;

FIG. 4 is an exploded perspective view illustrating the periphery of aside frame in the seat frame;

FIG. 5 is a front view illustrating a positional relation among a sideframe, a connection frame, and a reclining mechanism;

FIG. 6 is a perspective view illustrating a state where the side frameand the connection frame are bonded to each other;

FIG. 7 is a side view illustrating a welding position between the sideframe and the connection frame;

FIG. 8 is a cross-sectional view illustrating a structure of the sideframe when taken along the line A-A of FIG. 3;

FIG. 9 is a cross-sectional view illustrating the connection frameattached to the side frame when taken along the line B-B of FIG. 3;

FIG. 10 is an external perspective view illustrating an actuatoraccording to the embodiment of the invention;

FIG. 11 is a side view illustrating a positional relation among the sideframe, the connection frame, and the actuator;

FIG. 12 is a top view illustrating the actuator and the peripherythereof;

FIG. 13 is a schematic side view illustrating a modified example of thevehicle seat according to the embodiment of the invention; and

FIG. 14 is a side view illustrating a modified example of a positionalrelation among the side frame, the connection frame, and the actuator.

DETAILED DESCRIPTION

Hereinafter, a seat frame for a vehicle seat according to variousembodiments of the invention will be described with reference to FIGS. 1to 14. Furthermore, in FIGS. 2, 4, 5, 6, 7, 8, and 9, an actuator and abolt for fixing the actuator are not illustrated in the drawings inorder to comprehensively illustrate the structure of the seat frame.Further, for convenience of description, a height adjustment mechanism 4and a slide rail mechanism R to be described later are not illustratedin FIG. 2.

In the description below, the front to back direction is a directionthat matches the traveling direction of the vehicle. Further, the widthdirection is a direction that extends along the width of the vehicle,more specifically, the right and left direction, and corresponds to thewidth direction of the vehicle seat of the invention. Further, the upand down direction is the up and down direction of the vehicle seat.Furthermore, in the description below, the position or posture of eachportion of the seat will be described based on a normal state, that is,a seated state of an occupant unless otherwise specified.

First, a basic configuration of a vehicle seat and a seat frame(hereinafter, referred to as a main seat S and a main frame F) accordingto the embodiment of the invention will be described.

The basic structure of the main seat S is substantially the same as thatof a known vehicle seat, and in the embodiment, the main seat isparticularly used as a front seat disposed in front of a rear seat.However, the invention is not limited thereto, and may be applied alsoto a seat frame for a vehicle seat as a rear seat.

More specifically, the main seat S includes a seat back S1, a seatcushion S2, and a headrest S3 as main components as illustrated inFIG. 1. The main frame F which forms the frame of the main seat Sincludes a seat back frame F1 equipped in the seat back S1 and a seatcushion frame F2 equipped in the seat cushion S2 as illustrated in FIG.2. Further, a guide stay fs into which a pillar S3 a extending from thelower portion of the headrest S3 is inserted to thereby support the bodyof the headrest S3 is fixed to the upper portion of the seat back frameF1.

Further, most of the main frame F is formed by metal members andwelding, particularly, laser-welding is used as a method of bonding thecomponents of the frame. Each of the seat back frame F1 and the seatcushion frame F2 which are assembled by using such laser-welding isconfigured to form a rectangular frame as illustrated in FIG. 2.

Then, lower ends of side frames 11 which are provided at both ends ofthe seat back frame F1 in the width direction are assembled to rear endsof side frames 1 which are provided at both ends of the seat cushionframe F2 in the width direction. In the main frame F, the lower ends ofthe side frames 11 are assembled to the rear ends of the side frames 1via reclining mechanisms 3 illustrated in FIG. 4.

The reclining mechanisms 3 are operated when the occupant operates anoperation portion (not illustrated) to rotate the seat back S1 so thatthe seat back tilts forward or backward with respect to the seat cushionS2. In the main seat S, the reclining mechanism 3 is individuallyprovided in each of the side frames 11 which are provided at both endsof the seat back frame F1 in the width direction, and it is attached toa lower portion of an outer surface 12 a of each side frame 11 bylaser-welding. Further, the reclining mechanism 3 is welded to the rearend of the inner wall surface of the side frame 1 at the surfaceopposite to the welding side with respect to the side frame 11.

Each reclining mechanism 3 has a known structure and includes areclining mechanism body 3 a and a penetration shaft 3 b which extendsin the width direction while penetrating reclining mechanism body 3 a.Additionally, the penetration shaft 3 b rotates; thereby, a drivingmechanism (not illustrated) which is provided inside the body isoperated. By the operation of the driving mechanism, a portion of thereclining mechanism body 3 a, which is bonded to the side frame 11rotates about the penetration shaft 3 b relative to the oppositeportion, specifically, to a portion of the seat cushion frame F2, whichis bonded to the side frame 1. Accordingly, the side frame 11 to whichthe reclining mechanism 3 is attached rotates about the penetrationshaft 3 b relative to the seat cushion S2. That is, the seat back S1pivots about the penetration shaft 3 b relative to the seat cushion S2.

Here, the penetration shaft 3 b is a rotation shaft which rotates todrive the reclining mechanism 3 and is a pivot shaft about which theseat back S1 pivots relative to the seat cushion S2 by the recliningmechanism 3. Furthermore, in the main seat S, the penetration shaft 3 bis used as a common shaft between the reclining mechanism 3 attached toone side frame 11 and the reclining mechanism 3 attached to the otherside frame 11. That is, the penetration shaft 3 b penetrates a side wall12 of one side frame 11 and extends to the other side frame 11 along thewidth direction to further penetrate the side wall 12 of the same sideframe 11.

Also, as illustrated in FIG. 5, both ends of the penetration shaft 3 brespectively penetrate the corresponding reclining mechanism bodies 3 aand further penetrate the side frames 1 of the seat cushion frame F2,which are located at the side of the reclining mechanism bodies 3 a.That is, in the main seat S, the penetration shaft 3 b is rotatablyprovided while penetrating the side wall 12 of the side frame 11 and theside frame 1 in the width direction. In other words, the recliningmechanism 3 is attached to the side wall 12 while the penetration shaft3 b penetrates the side wall 12 of the side frame 11.

Furthermore, in the main seat S, the penetration shaft 3 b is rotated bypower applied by an actuator 50 as another member illustrated in FIG.10. Specifically, the penetration shaft 3 b is inserted in an insertionhole formed in an output shaft (not illustrated) of the actuator 50, andit is engaged with the output shaft. Thus, when the output shaft of theactuator 50 rotates, the penetration shaft 3 b which is inserted in theoutput shaft rotates. As a result, the driving force of the actuator 50is transmitted to the reclining mechanism 3 via the penetration shaft 3b so that the reclining mechanism 3 is operated.

In the main seat S, the actuator 50 is disposed at the opposite side tothe reclining mechanism 3 via the side wall 12 while being engaged witha portion 3 c of the penetration shaft 3 b, which is at the innerportion of the side wall in the width direction while penetrating theside wall 12 of the side frame 11.

Furthermore, the actuator 50 is fixed to the side frame 11 by a bolt toregulate the rotation of the actuator 50 relative to the side frame 11when the output shaft is rotated.

The slide rail mechanism R which slides on the main seat S relative tothe vehicle body floor in the front to back direction is disposed at thelower position of the seat cushion S2. Additionally, in the main seat S,a height adjustment mechanism 4 for adjusting the seat height isprovided between the seat cushion S2 and the slide rail mechanism R inthe up and down direction. The height adjustment mechanism 4 is operatedwhen the occupant operates an operation lever 5 illustrated in FIG. 1.

Specifically, the height adjustment mechanism 4 adjusts the seat heightby rotating a rotary link 6 connecting the seat cushion frame F2 and theslide rail mechanism R to each other by way of a driving force generatedby the operation of the operation lever 5.

More specifically, four rotary links 6 are provided in total to belocated at both ends of each of the front and rear ends of the seatcushion frame F2 in the width direction. One end of each rotary link 6is rotatably supported by a support portion Rx which is provided on anupper rail Ru of the slide rail mechanism R to protrude upward. Further,the other end of each rotary link 6 is rotatably attached to the sideframe 1 of the seat cushion frame F2.

A sector gear 7 a is formed at the rear rotary link 6 out of the rotarylinks 6, which is located at one end side of the rotary links 6 in thewidth direction, and a pinion gear 7 b engages with the sector gear 7 a.The pinion gear 7 b is connected to the operation lever 5 by aconnection shaft (not illustrated). Accordingly, when the operationlever 5 is operated, the pinion gear 7 b rotates along with theconnection shaft so that the engagement position between the pinion gear7 b and the sector gear 7 a changes. In accordance with this change ofthe engagement position, the rotary link 6 provided with the sector gear7 a rotates, and the other rotary link 6 also rotates to follow therotation of the rotary link 6. As a result, the seat body including theseat cushion S2 is moved upward so that the seat height is adjusted.

Furthermore, in the main seat S, the operation lever 5 is set to belocated at the side of the seat cushion S2, and a brake mechanism (notillustrated) is provided between the side frame 1 of the seat cushionframe F2 and the operation lever 5. The brake mechanism applies afriction force to the connection shaft, connecting the operation lever 5and the pinion gear 7 b to each other, during a period in which theheight adjustment mechanism 4 is not driven, that is, the operationlever 5 is not operated. Accordingly, the unintended rotation of theconnection shaft is restricted so that the seat height is maintained.

Next, the seat back frame F1 of the main frame F will be described indetail.

As illustrated in FIGS. 2 and 3, the seat back frame F1 includes theside frames 11 which are disposed at both ends of the seat back frame F1in the width direction, an upper frame 21 which connects the upper endsof the side frames 11, and a lower member frame 31 which serves as aconnection frame connecting the lower ends of the side frames 11 to eachother.

As illustrated in FIGS. 2 and 3, the upper frame 21 is a portion thatforms the upper end of the seat back frame F1. The upper frame 21includes a bent portion 22 which is bent in a downward U-shape so thatboth ends of the upper frame 21 are directed downward, and an uppermember frame 23 which is laid between one end of the bent portion 22 andthe other end thereof.

The bent portion 22 is formed by bending a metallic pipe. Further, twocrushed areas are formed in the extension portion of the bent portion 22in the width direction so that flat surfaces are formed at the frontside of the bent portion 22. The crushed areas are formed at the bentportion 22 to be bilaterally symmetrical to each other, and theabove-described guide stays fs are fixed by laser-welding to the flatsurfaces which are formed at the front side of the crushed areas.

The upper member frame 23 is formed by processing a metal plate, and theends of the upper member frame 23 are respectively laser-welded to thedownwardly-extending bent ends of the bent portion 22. Furthermore,plural rectangular openings 23 a are formed at predetermined intervalsin an area located at the center portion of the upper member frame 23 inthe extension direction.

The side frames 11 are portions which form both ends of the seat backframe F1 in the width direction and extend in the up and down direction.In the main seat S, each side frame 11 is substantially bent in an arcshape so that the upper end is slightly located behind the lower end asillustrated in FIG. 2. Further, in the main seat S, each side frame 11is formed as a single member, and is specifically formed by processingone metal plate.

The structure of each side frame 11 will be described in more detail.Furthermore, since the side frames 11 which are disposed at both ends inthe width direction are configured to be bilaterally symmetrical to eachother, only the structure of one side frame 11 will be described below.

As illustrated in FIG. 8, each side frame 11 includes the side wall 12which is located at the outward in the width direction and a rear wall13 which extends inward in the width direction from the rear end of theside wall 12. The side wall 12 extends substantially straight in the upand down direction. When viewed from the side in the width direction,the side wall is configured so that the upper end is formed in a pointedshape which narrows toward its upper end, that the center portion isformed in a smoothly curved shape, and that the lower end is formed in asemi-oval shape.

The side wall 12 is provided with plural holes. One hole 12 c of theplural holes is formed at the lower end of the side wall 12, and thepenetration shaft 3 b for driving the reclining mechanism 3 is insertedinto the hole 12 c. Further, the other hole is a bolt hole 12 d which islocated above the hole 12 c into which the penetration shaft 3 b isinserted, and a bolt 51 for stopping the rotation of the actuator 50 isinserted into the bolt hole 12 c. In addition, one of the remainingholes is a hole for fixing the side frame 11 when the seat back frame F1is assembled, in particular, when members configuring the seat backframe F1 are welded, and a fixing jig (not illustrated) used for thewelding operation is inserted into the hole 12 c.

Further, as described above, the reclining mechanism 3 is attached tothe outer surface 12 a of the side surfaces of the side wall 12, whichis located at the outward in the width direction. More specifically, inthe main seat S, the reclining mechanism 3 is attached by laser-weldingto a portion which is located slightly above the lower end of the sidewall 12. Here, in a case where the reclining mechanism 3 is attached tothe outer surface 12 a of the side wall 12 by laser-welding, the laseris radiated to an inner surface 12 b of the side surface of the sidewall 12, which is located at the back side of the outer surface 12 a inthe width direction. Therefore, unevenness is formed as a welding markon the inner surface 12 b.

Furthermore, in the main seat S, a portion of the reclining mechanism 3,which is bonded to the side wall 12 of the side frame 11, morespecifically, a portion of the reclining mechanism body 3 a, which facesthe side wall 12, is formed in a circular shape. Thus, in the main seatS, an area in which the reclining mechanism 3 is attached to the outersurface 12 a of each side wall 12 of the side frame 11 is formed as acircular area M when viewed from the width direction as illustrated inFIG. 7. Furthermore, a hole into which the penetration shaft 3 b isinserted is formed at the center position of the circular area M.

Further, as illustrated in FIGS. 4 and 8, a side wall side flange 14which is bent inward in the width direction is formed at the front endof the side wall 12. The side wall side flange 14 corresponds to a sidewall side bent portion, and it is formed from the upper end of the sidewall 12 to the lower end thereof in order to reinforce the side wall 12.Here, the lower end of the side wall 12 is formed in a semi-oval shapeas described above, and the side wall side flange 14 which is providedat the lower end of the side wall 12 is formed in a circular-arc shapeto wrap around the outer edge of the lower end of the side wall 12 fromthe front side to the rear side.

The rear wall 13 is adjacent to the rear end of the side wall 12 whileintersecting the side wall 12, and in the main seat S, an angle of about90° is formed between the rear wall 13 and the side wall 12. In otherwords, the outer end of the rear wall 13 in the width direction forms acorner of the side frame 11 along with the rear end of the side wall 12.

Further, the upper end of the rear wall 13 is slightly lower than theupper end of the side wall 12, and the lower end of the rear wall 13 isslightly higher than the lower end of the side wall 12. Additionally, asillustrated in FIG. 3, the lower end of the rear wall 13 is providedwith a member frame attachment portion 13 a which is substantiallyformed in a trapezoid shape and of which the inward extension portion inthe width direction is larger than that of a portion above the memberframe attachment portion. The lower member frame 31 to be describedlater is attached to the member frame attachment portion 13 a.

Further, an elongated hole 16 is formed at a boundary portion betweenthe side wall 12 and the rear wall 13, that is, at the corner of theside frame 11, to be substantially horizontal across both the side wall12 and the rear wall 13. The elongated hole 16 is formed at the cornerof the side frame 11; thereby, the side frame 11 is easily deformed tobe inclined backward, for example, when a collision load is applied tothe vehicle equipped with the main seat S from the rear side. That is,the elongated hole 16 corresponding to a fragile portion is deformedfirst in the side frame 11 when a collision load is applied from therear side (in a precise sense, the elongated hole is deformed to becrushed in the up and down direction), and it becomes a start point whenthe side frame 11 is deformed.

Further, as illustrated in FIGS. 4 and 8, the inner end of the rear wall13 in the width direction is provided with a rear wall side flange 15which is bent forward. The rear wall side flange 15 is formed downwardfrom the upper end of the rear wall 13 to reinforce the rear wall 13,and it is formed along the upper end of the member frame attachmentportion 13 a. Further, the rear wall side flange 15 is also formed in anarea which is located below the member frame attachment portion 13 a inthe rear wall 13. The flange 15 is not formed at the inner portion ofthe member frame attachment portion 13 a in the width direction and atthe lower end side portion of the outer edge of the member frameattachment portion 13 a for the purpose of preventing the interferenceof the member frame attachment portion 13 a with the lower member frame31.

Furthermore, as illustrated in FIG. 4, the rear wall side flange 15formed at the lower end of the rear wall 13 is configured so that itsoutward end in the width direction is formed continuously to the sidewall side flange 14 which is formed at the lower end of the side wall 12to be deflected toward the rear side thereof. Therefore, the rigidity ofthe entire side frame 11 is further improved.

As illustrated in FIGS. 2 and 9, the lower member frame 31 issubstantially formed in a U-shape when viewed from the upside, and it isformed by processing one metal plate. The lower member frame 31 includesa first extension portion 32 which extends in the width direction and asecond extension portion 33 which extends forward from both ends of thefirst extension portion 32 in the width direction.

The first extension portion 32 is a portion which is disposed betweenthe side frames 11 in the width direction, and it is attached toparticularly the above-described member frame attachment portion 13 a ofthe rear wall 13 of the side frame 11. More specifically, both ends ofthe first extension portion 32 in the extension direction are attachedto the member frame attachment portion 13 a by laser-welding while beingin contact with the front surfaces of the member frame attachmentportions 13 a.

Furthermore, in the main seat S, the lower member frame 31 is attachedto a portion of the side frame 11, which is located below the portionprovided with the elongated hole 16. That is, the lower member frame 31is attached to the side frame 11 at a position avoiding the elongatedhole 16 in the up and down direction. Accordingly, an effect that therigidity is improved by the attachment of the lower member frame 31 isdifficult to be obtained in the vicinity of the elongated hole 16;therefore, the elongated hole 16 is easily deformed when a collisionload is applied from the rear side.

Further, as illustrated in FIG. 6, the end of the first extensionportion 32 in the extension direction is provided with a hole 32 b whichcommunicates with a through-hole (not illustrated), formed in the memberframe attachment portion 13 a, in a state where the first extensionportion 32 is attached to the member frame attachment portion 13 a. Thehole 32 b is a hole which is used to fix the lower member frame 31 whenthe seat back frame F1 is assembled, in particular, when the membersconfiguring the seat back frame F1 are welded, and a fixing jig (notillustrated) is inserted into the same hole 32 b during a weldingoperation.

The shape of the first extension portion 32 will be described in moredetail. As illustrated in FIG. 3, the lower end position of the firstextension portion 32 at the center portion in the extension direction islocated slightly above the lower end position of the end in theextension direction. That is, in the main seat S, the first extensionportion 32 is formed in a shape so that the lower end is slightly raisedat the center portion in the extension direction. Since the firstextension portion 32 having such a shape is provided, the main seat Smay be easily used as a front seat.

An illustration for clarity is a case in which the legs of the occupantsitting on the rear seat may enter a space located below the lowermember frame 31 of the front seat. Here, if the first extension portion32 of the lower member frame 31, which is located above the legs of theoccupant, is provided so that the lower end of the center portion in theextension direction is located above the lower end of the end in theextension direction, a problem that the legs of the occupant interferewith the lower member frame 31 can be avoided.

The end of the first extension portion 32 in the extension direction iswider than the center portion in the extension direction in the up anddown direction, and hence the rigidity of the lower member frame 31 isensured.

Further, as illustrated in FIG. 3, a bulged portion 32 a which is bulgedin a circular-arc shape from the front surface (in other words, aportion of the rear surface, which is depressed in a circular-arc shape)is formed at the center portion of the first extension portion 32 in theup and down direction. The bulged portion 32 a is a so-calledreinforcement bead, and it is formed in a slightly elongated shape inthe extension direction of the first extension portion 32.

Further, as illustrated in FIG. 4 or 6, the upper end of the firstextension portion 32 is provided with a first extension portion upperflange 34 which is bent forward. The first extension portion upperflange 34 is formed from one end of the first extension portion 32 tothe other end thereof in the extension direction in order to reinforcethe first extension portion 32.

Moreover, in the main seat S, as illustrated in FIG. 6, the rear wallside flange 15 (particularly, the inner end of the flange 15 in thewidth direction) which is formed at the upper end of the member frameattachment portion 13 a is in contact with a portion of the firstextension portion upper flange 34, which is slightly close to the centerof the first extension portion 32 in relation to the end position of thefirst extension portion 32 in the extension direction. That is, in themain seat S, the lower member frame 31 is attached to the member frameattachment portion 13 a so that the rear wall side flange 15 and thefirst extension portion upper flange 34 are provided continuously toeach other. Therefore, the lower member frame 31 and the side frame 11are strongly integrated with each other, and hence the rigidity in thevicinity of the attachment portion of the lower member frame 31 in theside frame 11 is further improved.

Further, the lower end of the first extension portion 32 is providedwith the first extension portion lower flange 35 which is bent forwardand is formed from one end of the first extension portion 32 to theother end thereof in the extension direction. Therefore, the rigidity ofthe lower member frame 31 is further improved.

The second extension portion 33 is adjacent to each of both ends of thefirst extension portion 32 in the extension direction while intersectingthe first extension portion 32, and in the main seat S, an angle ofabout 90° is formed between the first extension portion 32 and thesecond extension portion 33. In other words, the rear end of the secondextension portion 33 forms a corner of the lower member frame 31 alongwith the end of the first extension portion 32 in the extensiondirection.

Then, in the main seat S, the lower member frame 31 is attached to themember frame attachment portion 13 a so that the corner of the lowermember frame 31 overlaps the corner of the side frame 11 as illustratedin FIG. 6. That is, the second extension portion 33 is located at theinside in the width direction in relation to the side wall 12 of theside frame 11 and overlaps the side wall 12. More specifically, thesecond extension portion 33 is attached to the side wall 12 bylaser-welding while being in contact with the inner surface 12 b of theside wall 12.

As described above, in the main seat S, since the second extensionportion 33 of the lower member frame 31 is disposed while being incontact with the inner surface 12 b of the side wall 12 of the sideframe 11, the rigidity of the side wall 12 of the side frame 11, inparticular, the rigidity with respect to the load particularly exertedin the width direction is improved, and hence the side frame 11 isprevented from tilting inward. That is, the second extension portion 33is disposed to overlap the inside of the side wall 12 of the side frame11; thereby, the rigidity can be improved to the extent that the sideframe 11 is prevented from tilting inward.

Further, in the main seat S, the second extension portion 33 serves asan attachment bracket used to attach the actuator 50 to the inside ofthe side wall 12 of the side frame 11 in the width direction asillustrated in FIG. 11. That is, in the main seat S, in the case ofattaching the actuator 50 to the inner surface 12 b of the side wall 12of the side frame 11, the attachment bracket is bonded to the inside ofthe side wall 12 in the width direction and the actuator 50 is fixed tothe attachment bracket. Specifically, the attachment bracket is providedwith a bolt hole 33 a, and the bolt 51 for stopping the rotation of theactuator 50 is inserted into the both bolt holes 12 d and 33 a while thebolt hole 33 a communicates with the bolt hole 12 d formed in the sidewall 12 of the side frame 11.

Additionally, in the main seat S, the second extension portion 33 of thelower member frame 31 serves as the attachment bracket. In other words,in the main seat S, the attachment bracket is disposed at each of bothends of the lower member frame 31, and is integrated with the lowermember frame 31. In this way, a portion of the lower member frame 31 isused as the attachment bracket; thereby, the number of components isreduced compared to the configuration in which the attachment bracket isprovided as a separate member.

The shape of the second extension portion 33 will be described in moredetail. As illustrated in FIGS. 6 and 7, the second extension portion 33has a C-shape when viewed from the width direction. That is, the centerportion of the second extension portion 33 provided in the main seat Sis punched in a circular shape. Further, a lower half area of the frontend of the second extension portion 33 is notched to be formedcontinuously to the circular punched portion. When such punching andnotching are performed, the second extension portion 33 includes anupper portion 36 which is disposed above the circular punched portionand a lower portion 37 which is disposed below the circular punchedportion. Additionally, both the upper portion 36 and the lower portion37 are bonded to the side wall 12 by laser-welding while being incontact with the inner surface 12 b of the side wall 12 of the sideframe 11.

The circular punched portion of the second extension portion 33 is notbonded to the side wall 12 of the side frame 11. Additionally, in themain seat S, the reclining mechanism 3 is disposed at the positionopposite to the circular punched portion in a state where the side wall12 is arranged between the circular punched portion and the recliningmechanism 3. That is, in the main seat S, an area in which the circularpunched portion is located in the side wall 12 of the side frame 11corresponds to an area in which the reclining mechanism 3 is attached tothe outer surface 12 a.

In other words, in the main seat S, an area in which the upper portion36 and the lower portion 37 of the second extension portion 33 are incontact with the inner surface 12 b in the side wall 12 of the sideframe 11 is separated from an area in which the reclining mechanism 3 isattached to the outer surface 12 a. Specifically, as described above,there is a case in which an unevenness as a welding mark generated bylaser-welding may be formed on the inner surface 12 b in the area inwhich the reclining mechanism 3 is attached to the outer surface of theside wall 12. The second extension portion 33 is attached to the innersurface 12 b of the side wall 12 while avoiding a portion at which suchunevenness is formed; therefore, the lower member frame 31 including thesecond extension portion 33 can be satisfactorily attached to the sidewall 12.

In the main seat S, the area in which the reclining mechanism 3 isattached to the outer surface 12 a in the side wall 12 is formed in acircular shape as viewed from the width direction as described above.The center portion of the second extension portion 33 of the lowermember frame 31 is punched in a circular shape to match the circulararea M. Additionally, in the main seat S, the second extension portion33 is bonded to the side wall 12 so that the outer edge of the circulararea M matches the inner edge of the circular punched portion in thesecond extension portion 33.

That is, in the main seat S, an area in which the second extensionportion 33 are in contact with the inner surface 12 b in the side wall12 is formed as a C-shaped area which follows the outer edge of thecircular area M when viewed from the width direction. More specifically,as illustrated in FIGS. 6 and 7, a portion which is located at the lowerside in the center portion of the upper portion 36 of the secondextension portion 33 in the front to back direction is notched in asemi-circular shape. Additionally, the second extension portion 33 isattached to the side wall 12 to follow the edge of the notch and theupper portion of the outer edge of the circular area M. In other words,the upper portion 36 is a portion which is disposed above the circulararea M in the second extension portion 33.

As illustrated in FIGS. 6 and 7, the lower portion 37 of the secondextension portion 33 extends forward in a circular-arc shape.Additionally, the second extension portion 33 is attached to the sidewall 12 so that the lower portion 37 follows the lower portion of theouter edge of the circular area M. In other words, the lower portion 37is a portion of the second extension portion 33, which is located belowthe circular area M, and it extends in a circular-arc shape along theouter edge of the circular area M.

As described above, in the main seat S, the second extension portion 33is formed in a C-shape that follows the outer edge of the circular areaM (the area in which the reclining mechanism 3 is attached in the sidewall 12 of the side frame 11) when viewed from the width direction. Inaddition, the second extension portion 33 is bonded to the side wall 12so that the circular area M matches the circular punched portion of thesecond extension portion 33. In contrast, in the case of bonding thesecond extension portion 33 to the side wall 12, the circular area M maybe matched to the circular punched portion of the second extensionportion 33. Therefore, an operation for attaching the lower member frame31 while avoiding the attachment portion of the reclining mechanism 3 inthe side wall 12 of the side frame 11 can be easily performed.

Particularly, in the case where the seat back frame F1 of the main seatS is assembled, the reclining mechanism 3 is first attached to the sidewall 12 of the side frame 11 by laser-welding, and then the lower memberframe 31 is attached to the side frame 11. If the circular area Mmatches the circular punched portion of the second extension portion 33when the seat back frame F1 is assembled according to such an assemblingorder, it is possible to more easily attach the lower member frame 31 toavoid the attachment portion of the reclining mechanism 3 in the sidewall 12 of the side frame 11. That is, in the case where the seat backframe F1 is assembled according to the above-described assembling order,it is more effective to punch the center portion of the second extensionportion 33 in a circular shape to follow the outer edge of the circulararea M.

Additionally, the rear ends of the upper portion 36 and the lowerportion 37 are connected to each other via a connection portion 40. Theconnection portion 40 is located behind an area in which the recliningmechanism 3 is attached in the side wall 12, and it is formed in a shapethat follows the outer edge of the corresponding area. The front ends ofthe upper portion 36 and the lower portion 37 are separated from eachother in the up and down direction.

As described above, the shape of the second extension portion 33 thatserves as the attachment bracket of the actuator is formed as a shapethat avoids an area in which the reclining mechanism 3 is attached inthe side wall 12 of the side frame 11. Accordingly, the second extensionportion 33 may be bonded to the inner surface 12 b of the side wall 12of the side frame 11 while avoiding the interference with the rotationshaft for driving the reclining mechanism 3, that is, the penetrationshaft 3 b. Further, since the front end of the second extension portion33 is opened, the second extension portion 33 may be easily bonded tothe inner surface 12 b of the side wall 12 while avoiding theinterference with the penetration shaft 3 b.

Furthermore, as described above, in the main seat S, since the secondextension portion 33 is formed in a C-shape that follows the outer edgeof the attachment area of the reclining mechanism 3 in the side wall 12of the side frame 11 when viewed from the width direction, the secondextension portion 33 may be effectively bonded to the inner surface 12 bof the side wall 12.

Further, in the main seat S, the lower portion 37 of the secondextension portion 33 extends in a circular-arc shape to wrap around fromthe rear side of the penetration shaft 3 b to the front side of thepenetration shaft 3 b in the state where the second extension portion 33is bonded to the side wall 12. Similarly, the upper portion 36 of thesecond extension portion 33 also extends from the rear side of thepenetration shaft 3 b to the front side of the penetration shaft 3 b.With such a configuration, the lower member frame 31 may be attached tothe side wall 12 of the side frame 11 while avoiding the attachmentportion of the reclining mechanism 3 in the side wall 12 of the sideframe 11 and further avoiding the interference with the penetrationshaft 3 b. Further, since a portion of which the rigidity is improved bythe attachment of the lower member frame 31 in the side wall 12 of theside frame 11 extends in the front to back direction, the rigidity ofthe side frame 11 with respect to the load exerted in the widthdirection is improved.

Further, in the main seat S, as described above, the upper portion 36and the lower portion 37 of the second extension portion 33 arerespectively bonded to the side wall 12 of the side frame 11 bylaser-welding. Additionally, in the main seat S, as illustrated in FIG.7, a welding area X1 between the upper portion 36 and the side wall 12extends in a circular-arc shape in the front to back direction so that aportion of the welding area X1 is located in front of the penetrationshaft 3 b. Similarly, a welding area X2 between the lower portion 37 andthe side wall 12 extends in a circular-arc shape in the front to backdirection so that a portion of the welding area X2 is located behind thepenetration shaft 3 b.

As described above, in the main seat S, since the welding areas X1 andX2 are formed to have certain lengths in the front to back direction,the upper portion 36 and the lower portion 37 of the second extensionportion 33 are respectively and satisfactorily fixed to the side wall 12of the side frame 11. Further, since the welding areas X1 and X2 extendin the front to back direction, it is possible to ensure the strengthwith respect to the load exerted in the front to back direction.Accordingly, even when the load exerted in the front to back directionacts on the side frame 11 or the lower member frame 31, it is possibleto stably maintain a state where the second extension portion 33 of thelower member frame 31 is bonded to the side wall 12 of the side frame 11by suppressing the detachment in the welding areas X1 and X2.

Furthermore, in the main seat S, the welding area X1 between the upperportion 36 and the side wall 12 is a circular-arc area which correspondsto about ⅓ of the circumference about the penetration shaft 3 b, and thewelding area X2 between the lower portion 37 and the side wall 12 is acircular-arc area which corresponds to about ⅙ of the circumference.Further, both welding areas X1 and X2 are separated from each other. Inthis way, both welding areas X1 and X2 are separated from each otherwhile not satisfying one revolution on the circumference about thepenetration shaft 3 b. For this reason, in the case where the seat backframe F1 is assembled, the welding operation may be more easilyperformed compared to the case where the welding areas are continuouslywelded by laser by one revolution of the circumference about thepenetration shaft 3 b.

Further, in the main seat S, as illustrated in FIG. 7 or 11, the bolthole 33 a is formed in the front end of the upper portion 36. The bolthole 33 a is formed to fix the actuator 50, and it is a hole into whichthe bolt 51 for stopping the rotation of the actuator 50 is inserted asdescribed above. Additionally, in the main seat S, as illustrated inFIG. 7, in the upper portion 36, a portion which is located between thebolt hole 33 a and the attachment area of the reclining mechanism 3 inthe side wall 12 is welded to the side wall 12.

In other words, in the main seat S, the welding area X1 between theupper portion 36 and the side wall 12 exists between the bolt hole 33 aand the penetration shaft 3 b for driving the reclining mechanism 3. Inthis way, when the welding area X1 exists between the bolt hole 33 a andthe penetration shaft 3 b, the positions of the bolt hole 33 a and thepenetration shaft 3 b may not easily change. For this reason, thepositional relation between the penetration the bolt 51 for fixing theactuator 50 and shaft 3 b is stabilized. As a result, the actuator 50 isdisposed stably at a position where the actuator may be continuouslyoperated in a normal state.

As illustrated in FIGS. 4 and 6, the upper portion 36 and the lowerportion 37 of the second extension portion 33 are respectively providedwith the flanges which are bent inward in the width direction.Specifically, the upper portion 36 of the second extension portion 33 isprovided with a second extension portion upper flange 38 of which theupper end is bent inward in the width direction. The second extensionportion upper flange 38 corresponds to a bent portion, and it is formedfrom the front end of the upper portion 36 to the rear end thereof inorder to reinforce the second extension portion 33.

As described above, since the reinforcement flange 38 is formed in theupper end of the upper portion 36 of the second extension portion 33,the rigidity of the lower member frame 31 is improved, and hence therigidity of the side frame 11 to which the frame 31 is attached is alsoimproved.

Furthermore, as illustrated in FIG. 4, the rear end of the secondextension portion upper flange 38 is continuous to the first extensionportion upper flange 34 which is formed in the upper end of the firstextension portion 32. Accordingly, the rigidity of the entire lowermember frame 31 is more improved.

Further, in order to avoid the interference between the second extensionportion upper flange 38 and the actuator 50, the front end of the secondextension portion upper flange 38 is notched as illustrated in FIG. 12.More specifically, in a portion (hereinafter, referred to as an adjacentportion 38 a) which is adjacent to the bolt hole 33 a of the upperportion 36 in the second extension portion upper flange 38, the inwardextension amount in the width direction is shortened compared to aportion (hereinafter, referred to as a non-adjacent portion 38 b) whichis not adjacent to the portion provided with the bolt hole 33 a. Sincethe adjacent portion 38 a faces the vicinity of the attachment portionof the bolt 51 in the actuator 50, the second extension portion upperflange 38 may be formed while suppressing the interference with theactuator 50 by the above-described configuration.

As illustrated in FIGS. 4 and 6, the lower portion 37 of the secondextension portion 33 is provided with a second extension portion lowerflange 39 of which the lower end is bent inward in the width direction.The second extension portion lower flange 39 corresponds to a secondextension portion side bent portion, and it is formed from the front endof the lower portion 37 to the rear end thereof in order to reinforcethe second extension portion 33. Here, as described above, since thelower portion 37 extends in a circular-arc shape to wrap around from therear side of the penetration shaft 3 b to the front side thereof, thesecond extension portion lower flange 39 also extends in a circular-arcshape.

Additionally, in the main seat S, as illustrated in FIG. 6, the frontend of the second extension portion lower flange 39 overlaps in the upand down direction the rear end extending in a circular-arc shape at thelower end position of the side wall 12 in the side wall side flange 14formed in the side wall 12 of the side frame 11 while the secondextension portion 33 is bonded to the side wall 12.

More specifically, the lower portion 37 of the second extension portion33 extends so that the second extension portion lower flange 39 followsthe side wall side flange 14 and the front end of the second extensionportion lower flange 39 overlaps the rear end of the side wall sideflange 14. That is, in the main seat S, the lower member frame 31 isattached to the side frame 11 so that the second extension portion lowerflange 39 is provided continuously to the side wall side flange 14.Accordingly, the lower member frame 31 is strongly integrated with theside frame 11, particularly the lower end of the side wall 12, and hencethe rigidity in the vicinity of the attachment portion of the lowermember frame 31 in the side frame 11 is further improved.

Further, as illustrated in FIG. 4, the rear end of the second extensionportion lower flange 39 is connected to the first extension portionlower flange 35 which is formed in the lower end of the first extensionportion 32. Accordingly, the rigidity of the entire lower member frame31 is further improved.

In the above-described embodiment, a configuration example of the seatframe for the vehicle seat according to various embodiments of theinvention has been described. However, the above-described embodiment ismerely an example for helping the comprehension, and it does not limitthe invention. That is, the shapes, the dimensions, the arrangement, andthe like of the above-described members may be modified and improvedwithout departing from the spirit of the invention, and the equivalentthereof is included in the invention.

Hereinafter, a modified example of the seat frame of the vehicle seat ofthe invention will be described. The vehicle seat (hereinafter, referredto as a seat HS according to the modified example) according to themodified example includes an armrest S4 which is provided in one end ofthe seat back S1 in the width direction as illustrated in FIG. 13 inaddition to the configuration like the vehicle seat according to theabove-described embodiment. The armrest S4 is rotatable with respect tothe seat back S1 in the up and down direction and the front to backdirection, and an armrest rotation shaft 9 as a rotation shaft thereofis supported by the side wall 12 of the side frame 11 as illustrated inFIG. 14. More specifically, the armrest rotation shaft 9 is supported bya portion located above the attachment portion of the recliningmechanism 3 or the lower member frame 31 in the side wall 12.

When the armrest S4 rotates, that is, the armrest rotates in a directionto tilts forward, a load is applied to a portion which is located infront of the armrest rotation shaft 9 in the side frame 11. For thisreason, it is desirable to improve the rigidity of the portion locatedin front of the armrest rotation shaft 9 in the side frame 11 comparedto the other portion. For this reason, in the seat HS according to themodified example, the upper portion 36 of the second extension portion33 of the lower member frame 31 is provided with an additional extensionportion 41 which extends upward toward the armrest rotation shaft 9 asillustrated in FIG. 14.

The additional extension portion 41 corresponds to an extension portion,is located in front of the armrest rotation shaft 9, and it is bonded tothe inner surface 12 b of the side wall 12 of the side frame 11 bywelding. Accordingly, the rigidity of the side frame 11, in particular,the rigidity of the portion located in front of the armrest rotationshaft 9 is improved with respect to the load generated by the rotationof the armrest S4.

Furthermore, in the seat HS according to the modified example, theadditional extension portion 41 is provided directly above the portionprovided with the bolt hole 33 a in the upper portion 36. Accordingly,it is possible to improve the attachment rigidity for the actuator 50 inthe second extension portion 33 of the lower member frame 31. Further,the upper end of the additional extension portion 41 does not reach thesupport position of the armrest rotation shaft 9 and is located slightlybelow the support position.

Further, as described above, the side wall 12 of the side frame 11 isprovided with plural holes, but the additional extension portion 41 isbonded to the side frame 11 while avoiding the holes to not block theseholes. Particularly, the rear end of the side wall 12 of the side frame11 is provided with the elongated hole 16 which serves as a fragileportion deformed so that the side frame 11 is inclined backward when acollision load is applied from the rear side. Additionally, theadditional extension portion 41 is provided at the front position of theelongated hole 16 as illustrated in FIG. 14. With such a positionalrelation, even when the additional extension portion 41 is provided, theadditional extension portion does not influence the elongated hole 16,and hence the elongated hole 16 is satisfactorily deformed when thecollision load is applied from the rear side.

The assembly described herein may be applied also to a case other thanthe above-described embodiment. For example, in the above-describedembodiment, the second extension portion 33 of the lower member frame 31are in contact with the inner surface 12 b in the side wall 12 of theside frame 11. An area in which the reclining mechanism 3 is attached tothe outer surface 12 a in the side wall 12 is formed as the circulararea M when viewed from the width direction. Additionally, an area inwhich the second extension portion 33 are in contact with the innersurface 12 b in the side wall 12 is formed as the C-shaped area thatfollows the outer edge of the circular area M when viewed from the widthdirection. That is, the second extension portion 33 includes the upperportion 36 which is disposed above the circular area M and the lowerportion 37 which is disposed below the circular area M. However, theinvention is not limited thereto, and the second extension portion 33may include only a portion corresponding to any one of the upper portion36 and the lower portion 37.

Further, in the above-described embodiment, each of the upper portion 36and the lower portion 37 is provided with the reinforcement flange (thesecond extension portion upper flange 38 and the second extensionportion lower flange 39), but the invention is not limited thereto. Forexample, a configuration may be employed also in which the reinforcementflange is not provided.

Further, in the above-described embodiment, laser-welding is used as amethod of boding the components of the main frame F, but the inventionis not limited thereto. For example, the other welding methods (forexample, TIG welding, MIG welding, and arc welding) may be used.

Further, in the above-described embodiment, the front ends of the upperportion 36 and the lower portion 37 are separated from each other andthe rear ends thereof are connected to each other. However, theinvention is not limited thereto, and a configuration may be employed inwhich the rear ends of the upper portion 36 and the lower portion 37 areseparated from each other and the front ends thereof are connected toeach other.

TABLE OF REFERENCE NUMERALS S main seat S1 seat back S2 seat cushion S3headrest S3a pillar S4 armrest F main frame F1 seat back frame F2 seatcushion frame fs guide stay R slide rail mechanism Ru upper rail Rxsupport portion M circular area X1, X2 welding area HS seat according tomodified example  1 side frame  3 reclining mechanism  3a recliningmechanism body  3b penetration shaft  3c penetration shaft portion  4height adjustment mechanism  5 operation lever  6 rotary link  7a sectorgear  7b pinion gear  9 armrest rotation shaft 11 side frame 12 sidewall 12a outer surface 12b inner surface 12c hole 12d bolt hole 13 rearwall 13a member frame attachment portion 14 side wall side flange 15rear wall side flange 16 elongated hole 21 upper frame 22 bent portion23 upper member frame 23a opening 31 lower member frame 32 firstextension portion 32a bulged portion, reinforcement portion 32b hole,through-hole 33 second extension portion 33a bolt hole 34 firstextension portion upper flange 35 first extension portion lower flange36 upper portion 37 lower portion 38 second extension portion upperflange 38a adjacent portion 38b non-adjacent portion 39 second extensionportion lower flange 40 connection portion 41 additional extensionportion 50 actuator 51 bolt

1. A vehicle seat comprising: a seat back frame, wherein: the seat backframe comprises side frames that are disposed at both ends of the seatback frame in a seat width direction of the vehicle seat, and a lowermember frame that connects lower ends of the side frames and is formedof a plate-shaped member; a reinforcement portion that extends along theseat width direction is provided at a portion of the lower member frameextending along the seat width direction; an upper flange is provided atan upper portion of the lower member frame, wherein the upper flange isformed by bending an upper end portion of the lower member frame; theupper flange is disposed on an upper side of the reinforcement portion;each of the side frames includes a side wall and a rear wall thatextends inward in the seat width direction from a rear end of the sidewall; a rear wall side flange is provided at an inner end of the rearwall in the seat width direction; and the upper flange extends to anoutside of the rear wall side flange in the seat width direction.
 2. Thevehicle seat according to claim 1, wherein: a protruding amount of theupper flange at a lateral end of the lower member frame in the seatwidth direction is smaller than a protruding amount of the upper flangeat a central portion of the lower member frame in the seat widthdirection.
 3. The vehicle seat according to claim 1, wherein: the upperflange extends to a position that overlaps one of the side frames; and aprotruding amount of the upper flange at a lateral end of the lowermember frame in the seat width direction is smaller than a protrudingamount of a portion of the upper flange at a central portion relative toa portion of the upper flange in the seat width direction positionedoverlapping the one of the side frames.
 4. The vehicle seat according toclaim 1, wherein: a protruding amount of the upper flange at a lateralend of the lower member frame in the seat width direction is smallerthan a protruding amount of a portion of the upper flange positionedoverlapping the reinforcement portion in an up and down direction. 5.The vehicle seat according to claim 1, wherein: each of the side framesis provided with a fragile portion; and the fragile portion is disposedbetween the upper flange and the rear wall side flange in an up and downdirection.
 6. The vehicle seat according to claim 1, wherein: athrough-hole is provided at the portion of the lower member frameextending along the seat width direction; and a length of thethrough-hole in an up and down direction is smaller than a length of thereinforcement portion in the up and down direction.
 7. The vehicle seataccording to claim 1, wherein: a through-hole is provided at the portionof the lower member frame extending along the seat width direction; andthe through-hole is circular and each lateral end of the reinforcementportion in the seat width direction has a circular arc shape.
 8. Amethod for manufacturing a vehicle seat having a seat back frame,comprising: arranging side frames of the seat back frame at both ends ofthe seat back frame in a seat width direction of the vehicle seat;arranging a lower member frame that is formed of a plate-shaped memberbetween the side frames; and connecting lower ends of the side frames bythe lower member frame, wherein: a reinforcement portion that extendsalong the seat width direction is provided at a portion of the lowermember frame extending along the seat width direction; an upper flangeis provided at an upper portion of the lower member frame, wherein theupper flange is formed by bending an upper end portion of the lowermember frame; the upper flange is disposed on an upper side of thereinforcement portion; each of the side frames includes a side wall anda rear wall that extends inward in the seat width direction from a rearend of the side wall; a rear wall side flange is provided at an innerend of the rear wall in the seat width direction; and the upper flangeextends to an outside of the rear wall side flange in the seat widthdirection.